A broadcasting system for radio signals that can be utilized in audio, video or telemetry is desired for many applications. For example, this type of system would be extremely useful for low power wireless television systems. In addition, it is known that more spectrum is available particularly at the higher frequencies (gigahertz frequencies). It is also known that such higher frequency gigahertz systems have certain transmission issues exacerbated due to their short wavelength. For example, one issue with such gigahertz transmissions is rainfall attenuation. Also, high transmitter power levels are difficult and expensive to generate at gigahertz frequencies.
Another issue is the requirement of a clear line of sight (LOS) path between the transmitting and receiving antennas when operating at gigahertz frequencies. The traditional approach to deal with this LOS requirement is to provide service from the top of the highest building (or tower) within the service area proper, using an omni-directional transmitting antenna. This traditional approach will often not be able to provide adequate total LOS coverage of the service area.
A multi-million dollar example of the risks associated with the loss of LOS under the traditional approach was the forced relocation of the high-power VHF/UHF commercial television stations, originally located atop the 102-story, 1,250' high Empire State Building in New York City, to the 110-floor, twin tower, 1,360' World Trade Center. While the difference in overall height of the buildings was only 110', the huge TV reception shadow cast behind the twin towers' constant cross-section structure was too massive to be tolerated and most of the Empire State site's TV antennas had to be moved. The Empire State Building now casts a shadow of its own, which damages direct incoming TV signal quality from the World Trade Center antennas in this new shadowed area, but to a far lesser extent due in part to the slender architectural shape of the Empire State Building's upper floors.
Existing wireless cable systems are known that employ polarization diversity to decrease interference distortion. Such a system would utilize an array of transmitters such that horizontally and vertically polarized omni-directional antennas alternate throughout the system. In such a system, each receiver with its appropriate narrow beam width antenna is directed at a specific transmitting antenna and is aligned to receive signals of the frequency and polarization of that transmitting antenna. Such a prior art system concerns itself with providing antennas of a specific polarization to improve reception. It is not concerned with or directed to the issues with LOS associated with high frequency transmissions. Accordingly, in those environments where the transmission paths were not LOS, the above-identified disclosure would still have serious coverage problems associated therewith.
What is needed therefore, is a system and method in which a broadcast system (audio, video or telemetry) can operate to provide extensive coverage of a particular service area. The method and system should be such that it can be easily implemented. Finally, the system should be a practical and cost effective solution to providing such broadcasting signals at high frequencies (1 gigahertz and greater); and to reduce reception problems due to loss of LOS which can be the result of structures, terrain, etc. The present invention addresses such a need.